Heat shrinkable film comprising polyester based copolymer

ABSTRACT

A heat shrinkable film comprising a polyester based copolymer is provided. The heat shrinkable film according to an exemplary embodiment of the present invention includes a polyester based copolymer, wherein the polyester based copolymer includes: a dicarboxylic acid-derived residue including a residue derived from an aromatic dicarboxylic acid; and a diol-derived residue including a residue derived from 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate represented by the following Chemical Formula 1 and a residue derived from 4,4-(oxybis(methylene)bis) cyclohexane methanol represented by the following Chemical Formula 2;

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. 371 and claims the benefit of PCT Application No. PCT/KR2014/005623 having an international filing date of Jun. 16, 2014, which designated the United States, which PCT application claimed the benefit of Korean Patent Application No. 10-2013-0069129 filed Jun. 17, 2013, the disclosures of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a heat shrinkable film comprising a polyester based copolymer, and more particularly, to a heat shrinkable film comprising a polyester based copolymer capable of having an excellent shrinkage rate and being heat shrunk at a low temperature.

BACKGROUND

A heat shrinkable plastic product uses a property of being shrunk by heating and is widely used as a film for a shrinkage package, a shrinkage label, or the like. Among them, polyvinyl chloride (PVC), polystyrene, and polyester based plastic films, and the like, have been used as a label or cap seal of various containers, or the like, or used as a direct package material, or the like.

However, a film made, of polyvinyl chloride is a regulation object since at the time of burning up the film, materials generating hydrogen chloride gas and dioxin may be generated. In addition, when this product is used as a shrinkage label of a polyethylene terephthalate (PET) container, or the like, at the reusing the container, a troublesome process of separating the label and the container should be performed.

Further, in the polystyrene based film, stability in work depending on a shrinkage process may be excellent and an appearance of the product may be good, but chemical resistance may not be excellent, such that there is a problem in that at the time of printing, an ink having a specific composition should be used. Further, the polystyrene based film has a disadvantage in that since storage stability at room temperature is insufficient, the film may be spontaneously shrunk, such that a dimension thereof may be changed.

In order to solve the above-mentioned problems, a film made of a polyester resin has been studied and developed as a film capable of replacing the films made of the above-mentioned two raw materials. Meanwhile, as a use amount of the PET container is increased, a use amount of a polyester film capable of being easily reused without separately separating a label at the time of reuse has been gradually increased, but a heat shrinkable polyester film according to the related art had a problem in view of shrinkage characteristics. That is, there was a problem in that wrinkles at the time of shrinkage or non-uniform shrinkage during molding was frequently generated due to a rapid change in shrinkage behavior. In addition, since a shrinkage property of the polyester film at a low temperature is decreased as compared to the polyvinyl chloride based film or the polystyrene based film, in order to complement this disadvantage, the polyester film should be shrunk at a high temperature. In this case, there was a problem in that PET container may be deformed, or a white-turbidity phenomenon may be generated.

Therefore, research into a polyester based copolymer of which a shrinkage rate is excellent and a shrinkage property at a low temperature is improved has been required.

DISCLOSURE Technical Problem

The present invention has been made an effort to provide a heat shrinkable film comprising a polyester based copolymer capable of having an excellent shrinkage rate and being heat shrunk at a low temperature.

Technical Solution

An exemplary embodiment of the present invention provides a heat shrinkable film comprising a polyester based copolymer, wherein the polyester based copolymer includes: a dicarboxylic acid-derived residue including a residue derived from an aromatic dicarboxylic acid; and a diol-derived residue including a residue derived from 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate represented by the following Chemical Formula 1 and a residue derived from 4,4-(oxybis(methylene)bis) cyclohexane methanol represented by the following Chemical Formula 2.

Further, the diol-derived residue may further include residues derived from 1,4-cyclohexane dimethanol, diethylene glycol, and ethylene glycol.

In addition, the aromatic dicarboxylic acid may be one or more selected from a group consisting of terephthalic acid, dimethyl terephthalate, cyclic dicarboxylic acid, isophthalic acid, adipic acid, azelaic acid, naphthalenedicarboxylic acid, and succinic acid.

The heat shrinkable film may have a shrinkage initiation temperature of about 65° C. or less, a maximum heat shrinkage rate thereof at 65° C. may be about 25% or more, and a maximum heat shrinkage rate thereof at 95° C. may be about 75% or more.

Another exemplary embodiment of the present invention provides a method for preparing a heat shrinkable film including: preparing a polyester based copolymer by reacting a dicarboxylic acid including an aromatic dicarboxylic acid with a diol including 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate represented by Chemical Formula 1 and 4,4-(oxybis(methylene)bis) cyclohexane methanol represented by Chemical Formula 2 to perform an esterification reaction and a polycondensation reaction; and extruding and drawing the polyester based copolymer.

The diol may further include 1,4-cyclohexane dimethanol, diethylene glycol, and ethylene glycol.

The diol may include about 0.1 to 10 mol % of 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate, about 0.1 to 12 mol % of 4,4-(oxybis(methylene)bis) cyclohexane methanol, about 0.1 to 15 mol % of 1,4-cyclohexane dimethanol, about 2 to 15 mol % of diethylene glycol, and about 48 to 97.7 mol % of ethylene glycol based on 100 mol % of the dicarboxylic acid.

The esterification reaction may be performed at a reaction temperature of about 230 to 265° C. and a pressure of about 1.0 to 3.0 kg/cm² for about 100 to 300 minutes after injecting the diol at a molar ratio of about 1.2 to 3.0 with respect to the dicarboxylic acid.

Further, in the esterification reaction and/or the polycondensation reaction, additives including a catalyst, a stabilizer, and a coloring agent may be used.

Meanwhile, the polycondensation reaction may be performed at a reaction temperature of about 260 to 290° C. and a reduced pressure of about 400 to 0.1 mmHg.

Advantageous Effects

The heat shrinkable film comprising a polyester based copolymer according to the present invention may have an excellent shrinkage rate as compared to a polyester based copolymer according to the related art, and be heat-shrunk at a low temperature, similarly to the PVC, thereby making it possible to prevent deformation of the PET container or the white-turbidity phenomenon that was caused in the heat shrinkage process of the film. In addition, since the shrinkage speed may be easily adjusted, such that the molding defect may be decreased.

BEST MODE

The present invention may be variously modified and have various exemplary embodiments, and specific embodiments of the present invention will be descried in detail. However, the present invention is not limited to specific exemplary embodiments described herein, but all of the modifications, equivalents, and substitutions within the spirit and scope of the present invention are also included in the present invention. Further, when it is determined that the detailed description of the known art related to the present invention may obscure the gist of the present invention, the detailed description thereof will be omitted.

According to an aspect of the present invention, there is provided a heat shrinkable film comprising a polyester based copolymer, wherein the polyester based copolymer includes: a dicarboxylic acid-derived residue including a residue derived from an aromatic dicarboxylic acid; and

a diol-derived residue including a residue derived from 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate represented by the following Chemical Formula 1 and a residue derived from 4,4-(oxybis(methylene)bis) cyclohexane methanol represented by the following Chemical Formula 2.

In addition, according to another aspect of the present invention, there is provided a method for preparing a heat shrinkable film including: preparing a polyester based copolymer by reacting a dicarboxylic acid including an aromatic dicarboxylic acid with a diol including 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate represented by Chemical Formula 1 and 4,4-(oxybis(methylene)bis) cyclohexane methanol represented by Chemical Formula 2 to perform an esterification reaction and a polycondensation reaction; and extruding and drawing the polyester based copolymer.

Hereinafter, the heat shrinkable film comprising a polyester based copolymer according to an exemplary embodiment of the present invention will be described in more detail.

As used herein, the term ‘residue’ means a predetermined moiety or unit included in a resultant of a chemical reaction when a specific compound participates in the chemical reaction, and derived from the specific compound. For example, the ‘dicarboxylic acid-derived residue’ and the ‘diol-derived residue’ mean moieties derived from a dicarboxylic acid component and a diol component in polyester formed by an esterification reaction or a polycondensation reaction, respectively.

An exemplary embodiment of the present invention provides a heat shrinkable film comprising a polyester based copolymer including a dicarboxylic acid-derived residue including a residue derived from an aromatic dicarboxylic acid; and a diol-derived residue including a residue derived from 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate represented by the following Chemical Formula 1 and a residue derived from 4,4-(oxybis(methylene)bis) cyclohexane methanol represented by the following Chemical Formula 2.

In a polyester film according to the related art, there was a problem in that due to a rapid change in shrinkage behavior, wrinkles at the time of shrinkage or non-uniform shrinkage during molding was frequently generated. In addition, since a shrinkage property of the polyester film at a low temperature is decreased as compared to the polyvinyl chloride based film or the polystyrene based film, in order to complement this disadvantage, the polyester film should be shrunk at a high temperature. In this case, there was a problem in that PET container may be deformed, or a white-turbidity phenomenon may be generated.

Therefore, the present inventors confirmed through experiments that in the case of using a diol including 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate and 4,4-(oxybis(methylene)bis) cyclohexane methanol, since a shrinkage rate was excellent and a polyester based copolymer may be heat-shrunk at a low temperature, similarly to a PVC, deformation of a PET container and a white-turbidity phenomenon that were caused in a heat shrinkage process of a film may be prevented, a molding defect may be decreased due to easiness to adjust a shrinkage rate, thereby completing the present invention.

As a diol compound used in order to improve moldability or other physical properties of a polymer prepared from terephthalic acid, diethylene glycol, and ethylene glycol, there are 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate, 4,4-(oxybis(methylene)bis) cyclohexane methanol, 1,4-cyclohexane dimethanol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexane dimethanol, 1,3-cyclohexane dimethanol, and the like. Particularly, as the diol compound used in order to improve physical properties of the polymer, 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate and 4,4-(oxybis(methylene)bis) cyclohexane methanol are preferable. The reason is that in the case of using 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate and 4,4-(oxybis(methylene)bis) cyclohexane methanol, since a molecular chain length at a predetermined level or more associated with residual stress is increased as compared to the case of using the above-mentioned compounds, residual stress depending on the drawing may be increased, such that at the time heat supply, shrinkage force may be increased in accordance with residual stress relaxation.

4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate is represented by the following Chemical Formula 1, and 4,4-(oxybis(methylene)bis) cyclohexane methanol is represented by the following Chemical Formula 2.

A use amount of 4-(hydroxymethyl)cyclohexylmethyl (hydroxymethyl)cyclohexane carboxylate and 4,4-(oxybis(methylene)bis) cyclohexane methanol used in the present invention is close to desired mol % in a final polymer. In order to prevent a moldability defect depending on crystallization, it is preferable that the use amount is about 2 to 17 mol % of the entire diol component. The reason is that in the case in which the use amount is less than about 2 mol %, it is difficult to confirm an effect of improving the shrinkage rate, and in the case in which the use amount is more than about 17 mol %, the white turbidity-phenomenon may be generated due to over-drawing, such that utility of the polyester based copolymer as a raw material for the heat shrinkable film is deteriorated.

Further, the diol-derived residue may further include residues derived from 1,4-cyclohexane dimethanol, diethylene glycol, and ethylene glycol.

In addition, the aromatic dicarboxylic acid may be one or more selected from a group consisting of terephthalic acid, dimethyl terephthalate, cyclic dicarboxylic acid, isophthalic acid, adipic acid, azelaic acid, naphthalenedicarboxylic acid, and succinic acid.

The heat shrinkable film as described above may have a shrinkage initiation temperature of about 65° C. or less, or about 20 to 60° C. In addition, a maximum heat shrinkage rate thereof at 65° C. may be about 25% or more, or about 25 to 35% or about 25 to 30%, and a maximum heat shrinkage rate thereof at 95° C. may be about 75% or more, about 75 to 90%, or about 75 to 80%.

The method for preparing a heat shrinkable film according to another aspect of the present invention may include: preparing the polyester based copolymer by reacting the dicarboxylic acid including the aromatic dicarboxylic acid with the diol including 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate represented by Chemical Formula 1 and 4,4-(oxybis(methylene)bis) cyclohexane methanol represented by Chemical Formula 2 to perform the esterification reaction and the polycondensation reaction; and extruding and drawing the polyester based copolymer.

In addition, the diol may further include 1,4-cyclohexane dimethanol, diethylene glycol, and ethylene glycol. That is, the diol may include about 0.1 to 10 mol % of 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate, about 0.1 to 12 mol % of 4,4-(oxybis(methylene)bis) cyclohexane methanol, about 0.1 to 15 mol % of 1,4-cyclohexane dimethanol, about 2 to 15 mol % of diethylene glycol, and about 48 to 97.7 mol % of ethylene glycol based on 100 mol % of the dicarboxylic acid.

The polyester based copolymer according to the present invention is prepared through the esterification reaction and the polycondensation reaction. The esterification reaction corresponding to a first step may be carried out batchwise or continuously, and each raw material may be separately injected, but preferably, the dicarboxylic acid may be injected into the diol in a slurry form.

In addition, the esterification reaction is performed at a reaction temperature of about 230 to 265° C., more preferably, about 245 to 255° C., and a pressure of about 1.0 to 3.0 kg/cm² after injecting the diol at a molar ratio of about 1.2 to 3.0 with respect to the dicarboxylic acid. Further, a reaction time of the esterification reaction may be generally about 100 to 300 minutes, but since the reaction time may be suitably changed according to the reaction temperature, the pressure, and the molar ratio of the glycol to the used dicarboxylic acid, the reaction time is not limited thereto.

Meanwhile, the esterification reaction does not require a catalyst, but in order to decrease the reaction time, a catalyst may be selectively injected.

After the above-mentioned esterification reaction is completed, the polycondensation reaction is carried out, and a catalyst, a stabilizer, a coloring agent, and the like, may be selectively used as components generally used at the time of polycondensation reaction of a polyester resin.

As a polycondensation catalyst usable in the present invention, there are titanium, germanium, and antimony compounds, and the like, but the present invention is not particularly limited thereto.

The titanium based catalyst, which is a catalyst used as a polycondensation catalyst of a polyester resin in which cyclohexane dimethanol based derivative is copolymerized at a ratio of 15% or more based on a weight of terephthalic acid, has advantages in that even in the case of using a small amount of the titanium based catalyst as compared to the antimony based catalyst, the polycondensation reaction may be carried out, and the titanium based catalyst is cheaper than the germanium based catalyst.

More specifically, as a usable titanium based catalyst, there are tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, polybutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, latate titanate, triethanolamine titanate, acetylacetonate titanate, ethylacetoacetic ester titanate, isostearyl titanate, titanium dioxide, coprecipitates of titanium dioxide and silicon dioxide, coprecipitates of titanium dioxide and zirconium dioxide, and the like.

In this case, since a use amount of the catalyst affects a color of the final polymer, the use amount may be changed according to the desired color, the used stabilizer, and the used coloring agent, but the use amount may be preferably about 1 to 100 ppm, more preferably, about 1 to 50 ppm, based on a content of a titanium element with respect to a weight of the final polymer, and may be about 10 ppm or less based on a content of a silicon element. The reason is that in the case in which the content of the titanium element is less than about 1 ppm, it is impossible to reach a desired degree of polymerization, and in the case in which the content is more than about 100 ppm, the final polymer becomes yellow, such that it is impossible to obtain a desired color.

Further, as other additives, the stabilizer, the coloring agent, and the like, may be used. As the stabilizer usable in the present invention, there are phosphoric acid, trimethyl phosphate, triethyl phosphate, triethylphosphonoacetate, and the like, and an addition amount thereof may be preferably about 10 to 100 ppm based on a content of a phosphorus element with respect to the weight of the final polymer. The reason is that in the case in which the addition amount of the stabilizer is less than about 10 ppm, it is difficult to obtain the desired bright color, and in the case in which the addition amount is more than about 100 ppm, it is impossible to reach a desired high degree of polymerization.

Further, as the coloring agent usable in the present invention in order to improve the color, there are cobalt acetate, cobalt propionate, and the like, and an addition amount thereof may be preferably about 100 ppm or less based on the weight of the final polymer. Furthermore, in addition to the coloring agent, an existing organic compound known in the art may be used as the coloring agent.

Meanwhile, the polycondensation reaction performed after adding these components may be preferably performed at about 260 to 290° C. and a reduced pressure of about 400 to 0.1 mmHg, but is not limited thereto.

The polycondensation step is performed until viscosity of the reactant reaches a desired inherent viscosity. In this case, a reaction temperature may be generally about 260 to 290° C., preferably about 260 to 280° C., and more preferably about 265 to 275° C.

Hereinafter, preferable Examples of the present invention will be described in detail. However, this example is only to illustrate the present invention and is not to be construed as limiting a scope of the present invention.

Example 1

A polyester resin in which 33 g of 4-(hydroxymethyl) cyclohexane carboxylic acid, 166 g of 4,4-(oxybis(methylene)bis) cyclohexane methanol, 22 g of 1,4-cyclohexane dimethanol, 162 g of diethylene glycol, and 1056 g of ethylene glycol were copolymerized based on 2312 g of terephthalic acid was slowly heated to 255° C. while being mixed in a batch reactor (3 kg), thereby performing a reaction.

In this case, an esterification reaction was performed by discharging generated water out of the reactor, and when generation and discharge of water were terminated, contents of the reactor were transferred to a polycondensation reactor equipped with a stirrer, a cooling condenser, and a vacuum system.

After 140 g of tetrabutyl titanate, 0.4 g of triethyl phosphate, and 19 g of cobalt acetate were added to the esterification resultant, a reaction was primarily performed for 40 minutes under a low vacuum (reduced from atmospheric pressure to 50 mmHg) while raising an internal temperature from 240° C. to 275° C. Then, ethylene glycol was removed, and the pressure was slowly reduced to 0.1 mmHg, such that the reaction was performed under a high vacuum until a desired viscosity was obtained. Thereafter, the resultant was ejected and cut in a chip form. A heat shrinkable film was prepared using the prepared polyester based copolymer.

Example 2

A heat shrinkable film was prepared by the same manner as in Example 1 except that 89 g of 4-(hydroxymethyl) cyclohexane carboxylic acid, 375 g of 4,4-(oxybis(methylene)bis) cyclohexane methanol, 33 g of 1,4-cyclohexane dimethanol, 162 g of diethylene glycol, and 976 g of ethylene glycol were injected, based on 2312 g of terephthalic acid.

Example 3

A heat shrinkable film was prepared by the same manner as in Example 1 except that 83 g of 4-(hydroxymethyl) cyclohexane carboxylic acid, 265 g of 4,4-(oxybis(methylene)bis) cyclohexane methanol, 112 g of 1,4-cyclohexane dimethanol, 162 g of diethylene glycol, and 976 g of ethylene glycol were injected, based on 2312 g of terephthalic acid.

Example 4

A heat shrinkable film was prepared by the same manner as in Example 1 except that 100 g of 4-(hydroxymethyl) cyclohexane carboxylic acid, 149 g of 4,4-(oxybis(methylene)bis) cyclohexane methanol, 167 g of 1,4-cyclohexane dimethanol, 162 g of diethylene glycol, and 985 g of ethylene glycol were injected, based on 2312 g of terephthalic acid.

Example 5

A heat shrinkable film was prepared by the same manner as in Example 1 except that 133 g of 4-(hydroxymethyl) cyclohexane carboxylic acid, 66 g of 4,4-(oxybis(methylene)bis) cyclohexane methanol, 268 g of 1,4-cyclohexane dimethanol, 162 g of diethylene glycol, and 959 g of ethylene glycol were injected, based on 2312 g of terephthalic acid.

Comparative Example 1

A heat shrinkable film was prepared by the same manner as in Example 1 except that 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate and 4,4-(oxybis(methylene)bis) cyclohexane methanol were not used, and 466 g of 1,4-cyclohexane dimethanol was injected.

Comparative Example 2

A heat shrinkable polyester film was prepared using a PVC resin.

Experimental Example

Glass transition temperatures, shrinkage initiation temperatures, heat shrinkage rates, and Inherent Viscosity of the heat shrinkable films and the polyester based copolymers prepared in Examples and Comparative Examples were measured by the following methods, and the measured results were shown in the following Table 1.

(1) Glass Transition Temperature (Tg): The glass transition temperature was measured using a differential scanning calorimetry (TA instrument Co.).

(2) Inherent Viscosity (IV): The inherent viscosity was measured using a Ubbelohde viscometer at a constant temperature bath of 35° C. after dissolving the prepared polyester based copolymer in ortho-chlorophenol at a concentration of 0.12% at 150° C.

(3) Heat Shrinkage Rate: After samples of the prepared films were cut into a square (10 cm×10 cm) and drawn at a draw ratio (DR) of 1:5 or 1:6 (MD:TD) and a draw speed of 20 mm/sec., the films were put into an oven at a temperature shown in Table 1 for 40 seconds to thereby be heat-shrunk. Thereafter, lengths of the samples in horizontal and vertical directions were measured, and the heat shrinkage rate was calculated by the following Equation. Heat shrinkage rate (%)=100×(length before shrinkage−length after shrinkage)/(length before shrinkage)

TABLE 1 Example Example Example Example Example Comparative Comparative 1 2 3 4 5 Example 1 Example 2 Glass Transition 66 67 67 68 68 69 65 Temperature (° C.) IV 0.69 0.7 0.72 0.72 0.71 0.7 Shrinkage Initiation 53 57 57 58 58 60 50 Temperature (° C.) Heat Shrinkage Rate 25 27 25 28 30 24 15 (%) at 65° C. Heat Shrinkage Rate 75 76 75 76 78 74 63 (%) at 95° C.

As shown in Table 1, since the heat shrinkable film made of the polyester based copolymer according to the present invention has a low shrinkage speed due to a low shrinkage initiation temperature, a process may be smoothly controlled, such that a defect rate may be decreased, and moldability may be excellent. Therefore, a heat shrinkable film product having excellent moldability may be obtained by molding the polyester based copolymer as described above through an extruding and drawing process.

Although the present invention has been described in detail based on particular features thereof, and it is obvious to those skilled in the art that these specific technologies are merely preferable embodiments and thus the scope of the present invention is not limited to the embodiments. Therefore, the substantial scope of the present invention is defined by the accompanying claims and equivalent thereof. 

What is claimed is:
 1. A method for preparing a heat shrinkable film, the method comprising: preparing a polyester based copolymer by reacting a dicarboxylic acid including an aromatic dicarboxylic acid with a diol including 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate represented by the following Chemical Formula 1, 4,4-(oxybis(methylene)bis) cyclohexane methanol represented by the following Chemical Formula 2, 1,4-cyclohexane dimethanol, diethylene glycol, and ethylene glycol to perform an esterification reaction and a polycondensation reaction; and extruding and drawing the polyester based copolymer, wherein the diol comprises between 0.1 mol % and 10 mol % of 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate, between 0.1 mol % and 12 mol % of 4,4-(oxybis(methylene)bis) cyclohexane methanol, between 0.1 mol % and 15 mol % of 1,4-cyclohexane dimethanol, between 2 mol % and 15 mol % of diethylene glycol, and between 48 mol % and 97.7 mol % of ethylene glycol, wherein a use amount of the 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate and the 4,4-(oxybis(methylene)bis) cyclohexane methanol is between 2 mol % and 17 mol % of the diol component, wherein the heat shrinkable film has a maximum heat shrinkage rate of 25% or more at 65° C. and a maximum heat shrinkage rate of 75% or more at 95° C.


2. The method of claim 1, wherein the esterification reaction is performed at a reaction temperature of 230 to 265° C. and a pressure of 1.0 to 3.0 kg/cm² for 100 to 300 minutes after injecting the diol at a molar ratio of 1.2 to 3.0 with respect to the dicarboxylic acid.
 3. The method of claim 1, wherein in the esterification reaction or the polycondensation reaction, additives including a catalyst, a stabilizer, and a coloring agent are used.
 4. The method of claim 1, wherein the polycondensation reaction is performed at a reaction temperature of 260 to 290° C. and a reduced pressure of 400 to 0.1 mmHg. 